β-Endorphin (human) (trifluoroacetate acid)

β-Endorphin is an endogenous 31-amino acid neuropeptide and opioid receptor agonist that binds to μ-, δ-, and κ-opioid receptors (Kis = 3.73, 5.02, and 32.7 nM, respectively, in COS-1 cells expressing rat receptors). It binds to rat and mouse brain membrane preparations (IC50s = 0.33 and 0.67 nM, respectively) and induces chemotaxis of human monocytes in vitro when used at a concentration of 0.1 pM. Intracerebroventricular administration of β-endorphin increases the latency to tail withdrawal in response to thermal stimuli in mice with a median antinociceptive dose (AD50) value of 27 pmol per animal. It also increases preference for the drug-paired place in a conditioned place preference test when administered to rats intracerebroventricularly at a dose of 5 μg.